Trees are sensitive to extreme weather and environmental conditions. This sensitivity is visible in tree-ring widths and cell structure. In our study, we hypothesized that the sudden frost noted at the beginning of May in both 2007 and 2011 affected cambial activity and, consequently, the number and size of vessels in the tree rings. It was decided to test this hypothesis after damage to leaves was observed. The applied response function model did not show any significant relationships between spring temperature and growth. However, this method uses average values for long periods and sometimes misses the short-term effects. This is why we decided to study each ring separately, comparing them with rings unaffected by the late frost. Our study showed that the short-term effect of sudden frost in late spring did not affect tree rings and selected cell parameters. The most likely reasons for this are (i) cambial activity producing the earlywood vessels before the occurrence of the observed leaf damage, (ii) the forest micro-climate protecting the trees from the harsh frost and (iii) the temperature decline being too short-lived an event to affect the oaks. On the other hand, the visible damage may be occasional and not affect cambium activity and tree vitality at all. We conclude that oak is well-adapted to this phenomenon.Electronic supplementary materialThe online version of this article (doi:10.1007/s00484-015-1107-6) contains supplementary material, which is available to authorized users.
Background
The role of selenium (Se) in the management of type 2 diabetes mellitus (T2DM) remains unclear. We systematically assessed the effectiveness and safety of Se supplementation in adults with T2DM.
Methods
MEDLINE, EMBASE and the Cochrane Library were searched up to April 2018 for randomised controlled trials (RCTs) evaluating the effectiveness of Se against a comparator on DM‐related outcomes.
Results
Four RCTs (241 participants) were included. In individual RCTs, Se supplementation significantly reduced fasting insulin levels [mean difference (MD) = −3.6 μIU mL−1; 95% confidence interval (CI) = −6.36 to −0.84; MD = −5.8 μIU mL−1; 95% CI = −9.23 to −2.37], homeostasis model of assessment‐estimated insulin resistance (HOMA‐IR) (MD = −1; 95% CI = −1.79 to −0.21; MD = −1.6; 95% CI, −2.58 to −0.62) and homeostasis model of assessment‐estimated B cell function (HOMA‐B) (MD = −13.6; 95% CI = −23.4 to −3.8; MD = −22.6; 95% CI = −36.39 to −8.81). No effects of Se were noted on most of the other outcomes of interest. None of the RCTs assessed the mortality, diabetes‐related complications, non‐high‐density lipoprotein (non‐HDL), blood pressure and health‐related quality of life. The impact on HDL and fasting plasma glucose (FPG) was ambiguous. Only one adverse event (nausea) was reported as a reason for discontinuing the intervention; however, among the studies, the reporting was not accurate. Furthermore, only one RCT reported increase in FPG level in the Se group (MD = 36.38 mg dL−1; 95% CI = 15.39–57.37).
Conclusions
Currently, there is no evidence to support the effectiveness of Se supplementation in the T2DM population.
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